1. Field of the Invention
This invention relates generally to the fields of molecular biology and gene regulation and more specifically to regulatory elements that are present in genes involved in cell death.
2. Background Information
Cell death occurs by a variety of processes including, for example, programmed cell death and necrosis. The term "apoptosis" describes the morphological features of cells undergoing the process of programmed cell death, which is responsible for maintaining a steady-state level of cells in a self-renewing tissues. Under normal conditions, apoptosis assures that the number of dying cells in a tissue is roughly equivalent to the number of newly produced cells. However, in various disease states or as a result of an insult to a tissue, dysregulation of the process of apoptosis can occur. Similarly, various diseases states are associated with increased levels of cell death due to processes other than apoptosis.
In Alzheimer's disease, Parkinson's disease, Huntington's chorea, epilepsy, amyotrophic lateral sclerosis, stroke, ischemic heart disease, spinal cord injury and many viral infections, for example, abnormally high levels of cell death occur. In at least some of these diseases, there is evidence that the excessive cell death occurs through mechanisms consistent with apoptosis. Among these are 1) spinal cord injury, where the severing of axons deprives neurons of neurotrophic factors necessary to sustain cellular viability; 2) stroke, where after an initial phase of necrotic cell death due to ischemia, the rupture of dead cells releases excitatory neurotransmitters such as glutamate and oxygen free radicals that stimulate apoptosis in neighboring healthy neurons; and 3) Human Immunodeficiency Virus (HIV) infection, which induces apoptosis of T-lymphocytes.
In contrast, the level of apoptosis is decreased in cancer cells, which allows the cancer cells to survive longer than their normal cell counterparts. As a result of the increased number of surviving cancer cells, the mass of a tumor can increase even if the doubling time of the cancer cells does not increase. Furthermore, the high level of expression in a cancer cell of the bcl-2 gene, which is involved in regulating apoptosis and, in some cases, necrotic cell death, renders the cancer cell relatively resistant to chemotherapeutic agents and to radiation therapy.
The molecular mechanisms that regulate cell death are not well understood. It is now becoming clear, however, that several proteins such as Bcl-2 and a Bcl-2-related protein, termed "Bax," have a central role in apoptosis. Specifically, the expression of Bcl-2 in a cell blocks apoptosis, whereas the expression of Bax in a cell induces apoptosis. Thus, when Bcl-2 levels in a cell are decreased and/or when Bax levels are elevated, the rate of cell death is accelerated. Conversely, when Bcl-2 levels in a cell are increased and/or when Bax levels are decreased, apoptosis is inhibited. In addition, Bcl-2 also may be involved in the process of necrotic cell death.
The p53 tumor suppressor protein (p53) is another example of a protein that is involved in the process of apoptosis. The wild-type p53 protein induces apoptosis in a cell, whereas mutant p53 proteins do not induce apoptosis. Many cancers have mutations in the genes encoding p53 and, therefore, either do not express any p53 protein or express a mutant p53 protein. Thus, the absence of a wild-type p53 tumor suppressor in a cancer cell also can contribute to the low level of apoptosis that occurs in cancer cells.
The ability to manipulate the mechanism by which the genes involved in cell death are regulated would provide physicians with a potential target for therapies aimed at ameliorating the effects of diseases that are characterized by abnormal levels of cell death and also would allow for the development of methods to identify agents that can effectively regulate, for example, apoptosis in a cell. However, the mechanisms by which these genes are regulated in a cell have not yet been described. Thus, there exists a need to identify methods to manipulate the regulatory elements for genes involved in apoptosis. The present invention satisfies this need and provides related advantages as well.